In a special express reading of the necessary laws, Saeima managed to conclude ratification before it broke for its summer holidays.
Addressing the chamber, Foreign Minister Edgars Rinkevics said OECD membership would be "a signal to investors and businesses that Latvia adheres to the highest standards" in areas such as tax, fighting corruption and financial regulation.
"This si not the end point," Rinkevics said, adding that work still needed to be done in various areas, with Saeima's cooperation, in battling corruption and improving regulation of the financial sector.
Nor was OECD membership simply a matter of doing what others recommend in order to join the club, Rinkevics said.
"It is in our own interests to continue in this direction."
He also thanks the three prime ministers who have overseen the OECD accession process: Valdis Dombrovskis, Laimdota Straujuma and Maris Kucinskis.
Later in the day Saeima approved Latvia's membership in a second and final reading of the bill by 68 votes to 0.
Effectively that means Latvia's accession process is now all but over, with only the signature of President Raimonds Vejonis required to give full legal force.